340 Miscellaneous. 
the two formations has already been pointed out by Langenbeck *, 
who has also endeavoured to show that Guppy’s theories are unten- 
able. ; 
As regards the more special study of the reefs, I have chiefly 
devoted my attention to determining the way in which the reefs are 
composed of the various forms of corals, how the latter are distri- 
buted upon the reefs, and what is the nature of the bottom upon 
which they rest. I cannot here enter into details, but would lay 
special stress on two points only. The observation has already been 
noted in various quarters, that Stony Corals may be temporarily de- 
prived of water and exposed to the sun and the open air without 
perishing. I made precisely the same discovery upon the reefs near 
Dar-es-Salaam. Certain forms (Porites, Goniastrea, Celoria, Tu- 
biporc) lie for hours during the ebb-tide, which is a very low one 
in that region, freely exposed to the air, but live and thrive exceed- 
ingly. That this faculty is wanting in other forms is shown at 
once by the fact that a number of species are met with in the com- 
pany of those mentioned above, at the same altitude of the reef, but 
are there found only in holes and pools, so that they are always 
covered by water. 
The following observation is also important. I found at certain 
points of the reefs near Dar-es-Nalaam extensive banks of living 
corals, resting upon a foundation which was quiteloose. The latter 
consisted of detritus (sand and gravel), which was held together by 
sea-wrack, and in this wrack were numerous corals, some of which 
were of but little thickness, while others formed large blocks, of 
which, moreover, entire banks were composed. All these blocks 
lay loose upon the bottom; I was able, provided their weight was 
not so considerable as to offer resistance, to lift them up or roll them 
over with ease. This observation is interesting in so far as it has 
been maintained by J. Walther (doc. cit.), that coral-reefs could only 
become established upon a firm (rocky) bottom; which may, indeed 
be correct enough so far as regards the forms mentioned by him 
(the umbrella-shaped Madrepores). There are, nevertheless, forms 
of corals (I am here alluding to species of the genera Psammocora, 
Montipora, and Lophoseris) which are capable of thriving upon a 
looser bottom in large blocks and forming banks. Such banks may 
then again furnish a basis for other corals, 
In accordance with the negative shore-displacement I also found 
an old coral-bed above the present level of the sea. The one which 
IT examined in sztwis of quite recent date, yet older raised beds of this 
kind doubtless occur in the region in question. The coral structure 
is for the most part no longer recognizable in the fossil beds. 
The coral-fauna of Dar-es-Salaam is closely allied, as might at 
once be conjectured from its geographical position, to that of the 
Red Sea (cf. Klunzinger), Yet we here already find a few Pacific 
types, which are wanting in the Red Sea—dZool. Anzeiger, 
xv. Jabrg., no. 381 (Jan 11th, 1892), pp. 18-20. 
* Langenbeck, ‘ Die Theorien iiber die Entstehung der Koralleninseln 
&ce.’: Leipzig, 1890. 
